1. Field
The present disclosure relates generally to electrochemical energy storage devices, and more specifically to lithium-ion capacitors and their methods of production.
2. Technical Background
Capacitors, including double layer capacitors, have been utilized in many electrical applications where a pulse of power is required. Some lithium-ion capacitors may have a significantly higher power density than standard ultracapacitors. However, many ultracapacitors have a relatively low energy density for selected purposes.
Lithium-ion capacitors contain a faradaic electrode (anode) and an activated carbon electrode (cathode) where there are no faradaic reactions. These capacitors have advantages associated with a battery (with respect to their high energy density) and a capacitor (with respect to their high power capability). For instance, lithium-ion capacitors can provide higher operating voltage (˜3.8-4V) compared to an EDLC device voltage of 2.5 to 2.7V.
Lithium-ion capacitors have been proposed to address the insufficient energy density in ultracapacitors and other standard capacitors. For lithium-ion based capacitors, currently-proposed models require that a lithium metal electrode, in addition to a cathode and an anode, be incorporated into the device. The result is an electrochemical energy storage device with three electrodes (cathode, anode, and lithium metal electrode).
Such three electrode devices require the use of a porous cathode in conjunction with a mesh-type current collector in order to facilitate transport of lithium into and within the cell. The fabrication of porous electrodes and the construction of the overall three-electrode capacitor design can be complicated, and such a cell may be expensive to manufacture. Additionally, the presence of a lithium metal electrode in the capacitor presents design challenges, as lithium metal is potentially combustible in the presence of air.